Apparatus for reproducing electric signals, particularly television reproducers



INVENTOR.

June 14, 1949. A. H. ROSENTHAL APPARATUS FOR REPRODUCING ELECTRIC SIGNALS, PARTICULARLY TELEVISION REPRODUCERS Filed Oct. 28, 1944 ADOLPH H. RO5ENTHAL BY L A TTO/QNEY Patented June 14, 1949 APPARATUS FOR REPRODUCING ELECTRIC SIGNALS, PARTICULARLY TELEVISION RE- PRODUCERS Adolph H. Rosenthal, New York, N. Y., asslgnor'to Scophony Corporation of America, New York, N. Y., a corporation of Delaware Application October 28, 1944, Serial No. 560,776

6 Claims. (Cl. 250-164) This invention relates to apparatus for visibly 3 The invention comprises apparatus for visibly reproducing signals, and in particular television projection receivers in which an electron stream or beam upon which the signals are impressed, changes the optical qualities of the impinged screen which can be viewed directly.

It is an object of the invention to provide reproducers of the type hereinbefore defined which can be observed without darkening the room in which the reproducer is operated.

It is another object of the invention to utilise diffuse light in a room which may be day light or artificial light, for making visible, or aid the visibility of signals reproduced in screens of the type hereinbefore defined, and particularly screens the optical qualities of which are changed by signals impressed upon an electron beam.

It is a further object of the invention to increase the contrast effects in reprcducer screens of the type hereinbefore defined, and particularly in screens the optical qualities of which are changed by signals impressed upon an electron beam.

It is a general object of the invention to provide what I call a "day light reproducer oi signals impressed upon an electron beam for visibly reproducing signals representative of intelligence of any kind, and in particular television pictures or images which can be observed to full eiiect in day or room light and also utilises the latter for this purpose.

These and other objects of the invention will be more clearly understood when the specification proceeds with reference-to the drawings in which rather schematically Fig. 1 shows in crosssection and partly in elevation a part of a housing or compartment with a cathode-ray producer of signals representative of intelligence, and Figs. 2 to 5 cross sections through a portion of such a reproducer embodying various modifications ac-' cording to the invention.

Referring to Fig. 1, a cathode-ray tube in is arranged within compartment II. The screen structure of and within the tube, in which signals representative of intelligence are to be reproduced, faces aperture 3t through which the screen can be directly viewed by an observer 35. Aperture 34 may be covered, e. g. by a removable glass plate l2. An electron gun including a cathode and electrostatic focussing means as well as 2 electrostatic deflecting means is arranged within neck iii of tube ill in well known manner; it electromagnetic focussing and deflecting means are used, they are comprised in coil assembly ll around neck It.

The evacuated glass envelope of tube In is pro vided with a preferably fiat front wall [3 on the inside of which a layer it is arranged which essentially consists of ionic crystal material of the type which under the impingement or bum-- bardment by electrons changes locally its optical qualities by the creation therein of color or opacity centers and comprises, for instance, certain alkali and/or alkaline earth halides, as described more in detail in my Patent No. 2,330,171. These salts are preferably evaporated upon wall i3 or settled upon it from a suspension e. g. in alcohol.

Screen or layer it is sufiiciently translucent so that changes in its optical qualities and particularly color or opacity centers formed in it, are

visible to an observer 35 from the outside through wall [3. Layer it can be given a white appearance when illuminated by incident day or room light, for instance by proper control of the evaporation process mentioned above; thus quick evaporation, or small amounts of gases present during the evaporation process, cause the layer to assume a high albedo or whiteness. Color or opacity centers created in the layer or screen illuminated by diffuse light from the same side as it is viewed, Will therefore appear dark on a white background to an observer 35.

A coating 20 of electrically conductive material is applied to the inside of tube envelope i0 except its front wall I3 and neck [6. If graphite is used, it is precipitated from a proper solution, for instance a colloidal graphite solution known as aquadag. This coating usually forms also an anode of the tube for accelerating the electrons toward screen It, and is on a high positive electrlc potential. Electrons of a beam impinging upon and entering through the front face of layer It opposite glass wall l3, create color or opacity centers and are drawn in the layer toward its other side facing glass wall ill by the high potential on that side, and finally diffuse into coating 2|]. When the translucent layer is illuminated by diffuse room light from the same side as it is viewed, opacity centers thus created and travelling across the layer will be seen by an observer 35 against the white background formed by areas of the layer in which no opacity centers are created.

In certain cases, depending upon the crystal inadequate, or it can be too transparent.

material or itscrystallisation; the reflection power, albedo or whiteness of. screen H can i): such cases a backing to is. provided for, screen layer ll of a metal of high optical reflective or light scattering power and pervious to or. transparent to electrons. Metals which permit electrons to pass therethrough without appreciable or detrimental loss and also exhibit great light reflecting power, are forlnstance aluminum, beryllium, magnesium and other metals of light atomic weight; aluminum is preferred. Backing or layerv I is preferably deposited upon screen layer It by evaporating the selected metal or metals in well known manner, or produced by cathode sputtering the metal or metals upon the screen layer. Even a relatively thick aluminum layer, of a, thickness of about 5 microns, which is available in the market in the form of an aluminum foil, permits about 95% of the electrons impinging thereon at a velocity of 50,000 electron volts to pass therethrough. Smaller thicknesses down to e. g. 0.1 micron required for a highly reflective layer can be obtained by evaporation or sputtering and will exhibit a far greater electron permeability, particularly also for slower electrons of only a. few thousand volts velocity, and still be perfect reflectors of incident light.

If the set illustrated in Fig. 1 is also to reproduce sound, a loud speaker 33 can be arranged within compartment ll behind another aperture 32.

Instead of applying a reflecting backing l5 upon a screen layer ll formed on glass wall IS, a self-supporting arrangement can be made as illustrated in Fig. 2. In this exempliflcation of the invention, a metal foil l5, for instance an aluminum foil of about 5 micron thickness, is fastened to a stiff metal frame [8 mounted spaced from but close to wall i3 and connected with a terminal conductor 2! sealed at 22 through the envelope of tube It.

A crystalline screen layer It of the type hereinbefore described is applied upon metal foil on its side facing wall l3, for instance by evaporation or settling from a suspension. A thin electrically conductive layer is which is transparent to light, is applied to the other side of layer it and may consist of a conductive oxide, such as zinc oxide, or of a thin layer of metal either the same as used for foil l5 or for instance platinum, rhodium, etc. which e. g. is deposited by evaporation or in any other suitable manner as a layer of minute thickness upon the crystalline layer [8. Therspringy extension 36 of terminal conductor 31 passed through seal 38 contacts layer 19; terminal 31 is connected with a suitably high positive electric potential or may be connected with coating outside (or inside) the tube. If a somewhat lower positive potential is applied through terminal 2i to layer I5 than is applied through terminal 37 to layer 19, a substantially homogeneous electrical field is produced between layers [5, IS in and across screen layer i6, wherebyand particularly with larger tubes and screen layers-the uniform migration through and removal from the screen layer of electrons injected into the latter by a modulated cathode ray beam is improved.

One of the advantages of the embodiment of the invention illustrated in Fig. 2 consists in that the crystal layer it and the conductive transparent layer 19 can be applied to foil l5 outside and before assembly of the tube. Furthermore, the halo caused by reflection of light inside thin glass wall I3 is reduced compared with tubes on the glass wall It of which layer M is applied in direct optical contact with it, and hence an increase in contrast results.-

It will be appreciated that in this manner the dayor room-light is utilized to greater eflect for-illuminating and making visible the signals reproduced in screen layer It. The incident light passes screen layer It on its way to backing or reflector l5 once, and the opacity centers produced therein absorb a portion of that light;

upon reflection from the backing or reflector,

the light passes the screen layer a second time on its way out, and thereby another portion of it is absorbed by the opacity centers at the same screen area. Thereby the desired contrast between unaffected areas of the screen layer through which white dayor room-light is reflected and areas the optical qualities of which are changed, in particular rendered opaque by the opacity centers produced therein, is greatly increased and practically doubled.

A further advantage of the invention as illustrated consists in that the electron gun can be arranged co-axially with tube l0, i. e. perpendicular to screen layer l4. Thereby the least distortion in the reproduction of signals occurs compared with other arrangements which require positioning of the electron gun obliquely to the optical axis of the screen so as to permit visible light to be projected along that axis through the screen layer unobstructed by the gun. The latter asymmetrical arrangement causes certain keystone distortions which have to be corrected by compensating the scanning and focussing effects accordingly.

Referring to Fi 3, a portion of a cathode-ray tube is shown in which again a conductive coating 20 is applied inside tube envelope l0 and connected with conductive layer l9 of suitable oxide or of evaporated or sputtered metal inside front wall I3; layer 19 is substantially transparent to light. On top of layer IS a screen layer It of ionic crystal material of the type hereinbefore defined is formed with or without binder, preferably by evaporation or by settling from a suspension or solution thereof. On top of crystal layer M the reflecting metal layer i5 is formed which is pervious to electrons and consists e. g. of evaporated aluminum. Leading-in wire 2! passes glass seals 22 and is electrically insulated by the inner portion of the' sea] from coating 20; its springy end 23 contacts metal layer It. A suitable potential intermediate between the highest positive potential on electrode l9 and the cathode potential, is applied to wire 2| and thereby a substantially homogeneous electric field of desired strength created in and across screen layer it between metal layer 15 which acts as a reflector as well as an electrode, and the other electrode 49.

The invention is' also applicable to color reproduction of signals representative of intelligence, in particular color television. Fig. 4 illustrates a portion of a cathode-ray tube used for instance for color television reproduction of the additive type. On the inside of front wall l3 of tube 10 a color filter screen 26 is applied which consists of groups of alternate fllter sections or bands 21, 28, 29 parallel to picture lines. Assuming that the color picture is transmitted by three fundamental partial colors, for instance of suitable red, green and blue hue, each group of filter sections 21, 28, 28 will consist of a red. green and blue section, and each section substantially cover a picture line. On the back of screen filter 26 an insulating coating or sheet 30 is applied which is transparent to light, for instance a suitable varnish or a sheet of mica of extreme thinness. In back of andupon insulation 30, a conductive layer 19 is applied, for instance by sputtering metal upon insulating layer 30; layer. I9 is also transparent to light and serves as an electrode which is connected with a conductive coating 20 inside envelope l0. Upon and in back of layer I9, a screen layer ii the optical qualities of which can be changed by an impinging electron beam, such as of the type described hereinbefore for layer H in Fig. 1, is applied, and upon and in back of screen layer ll, metal backing i pervious to electrons and of high light reflecting power is applied in the manner hereinbefore described. Leading-in wire 2| passes glass seal 22, is insulated thereby from coating 20 and contacts backing 15 with a springy extension 23. Thus reflector I5 acts as an electrode on one side and metal layer I9 is another electrode on the opposite side of screen layer It, for the purposes and effects stated hereinbefore.

A cathode ray beam upon which the signals to be reproduced are impressed, is swept over backing i5 and passes therethrough into screen layer Hi, producing therein opacity centers in a way well known in the art and described more in detail in my Patent No. 2,330,171. With television transmission, the cathode-ray beam scans the screen structure lt, IE in concurrence with the transmitter and in such a manner that during one color field period only lines of the screen structure are scanned adjacent to the red filter sections 21, during the next color field period only lines adjacent to the green filter sections 28, and during the third color field period only lines adjacent to the blue filter sections 29. The incident dayor room-light passing wall i3 and the sections of filter 26 can be completely reflected by backing or reflector iii if no cathode-ray beam impinges the screen structure and add up to create the impression of white light for the observer. Upon scanning the screen structure in the manner indicated above, however, and depending upon the instantaneous intensity and position of the cathode ray beam, light of green, red or blue color passing the respective filter section 21, 28 or 29 will be absorbed to a greater or smaller degree along the lines just undergoing scanning by the modulated beam, and the combined reflection of light during a total frame scan comprised by the three color field scans described above, adds up in creating a proper additive color mixture for the observer. this color system can be employed in the case of suspension screens.

Other color systems in which e. g. the colors alternate in line or element frequency can of course be used. In all cases proper methods of scanning and modulation are to be applied which follow from the characteristics of the respective system and not form a subject matter of this invention.

While in the foregoing and with respect to the screen layers the optical qualities of which can be changed by an impinging modulated electron beam, the creation of a particularly defined electric field gradient in or across the screen layer has been described, obtained by applying proper potentials to its surfaces, Fig. 5 illustrates a feature of the invention in which such a defined field Similarly substantially homogeneous and of gradient is set up by an emission of secondary electrons from the back surface of the screen layer. To this end, a conductive coating 20 inside envelope I0 is electrically connected with an electrode I 9 inside and on wall l3; electrode I9 is transparent to light, and on top of it a layer ll of ionic crystal material of the type hereinbefore defined is formed. On top of layer M an optical high reflecting metal layer 15 pervious to electrons is applied in the manner and for the purposes hereinbefore described. On back of layer l5, another layer 3| of low secondary to primary electron emission ratio, for instance-consisting or carbon black, is applied. The highest positive potential is applied in this exemplification through leading-in wire 2!, passing seal 22, to coating 20 and electrode l9 and thereby to the surface of screen layer it in contact therewith. The opposite surface of screen layer I4 facing layer 3| will after operation of the tube has started, soon assume a negative potential with respect to that of electrode 59, between that of the source of electrons (cathode), and that of electrode l9, depending upon leakage resistance; this potential is maintained thereafter during operation of the tube. .This is due to the fact that at the start of operation more primary electrons of the cathode-ray beam enter layer 3i than secondary electrons leave it, until layer M has assumed an equilibrium potential at which the sum of primary electrons leaving the layer towards the crystal screen and secondary electrons being emitted therefrom, equals the total amount of entering primary electrons (minor effects of reflected primary electrons, etc. being neglected). The intermediate potential thus created on layer 3! is therefore well defined and, in cooperation with the fixed highest potential put on the other side of screen layer it, produces an electric field in and across layer M which is desired strength.

Useful screen potentials of the inner surface of screen layer I 4 can also be obtained without layer 3! of low secondary to primary electron emission ratio on metal layer i5. Most metal layers have a secondary to primary electron emission characteristic of such a form that for low and high voltages of the primary electrons the secondary to,primary electron emission ratio is smaller than one, whereas for intermediate velocities of the primary electrons this ratio is larger than one. Thus the curve representing the ratio of secondary to primary emission as a function of the velocity of the primary electrons will cut the straight line representing emission ratio one at a low voltage (usually below volts) and at a high voltage of a few thousand volts, depending upon the metal. For aluminum, for instance, the upper intersection occurs between 2000 and 3000 volts of the primary electrons. By giving the inner coating 20, which also acts as accelerating anode of highest potential for the beam electrons, and thereby the transparent conductive layer W a potential of say 500 volts above the potential of this upper point of intersection of the secondary emission ratio curve with the ratio one line, the primary electrons impinging upon the aluminum layer l5 will have a speed of 500 volts above the upper intersection speed, and therefore will produce a smaller num ber of secondary electrons; thereby the potential of aluminum layer I5 is changed to a potential more negative than the potential of the opposite electrode l9 and which it had at the beginning of the operation due to leakage through screen layer l4. Thus the potential of layer i is lowered from that of its initial value equalling that of layer I9 until it reaches the potential of the upper intersection point. It cannot become more negative because then more secondary electrons would be liberated and it would immediately revert to the potential of the: upper intersection point. Therefore layer IE will assume very soon an equilibrium potential equal to the potential oi the upper intersection point of the secondary emission curve of its material, and since the opposite layer is is fixed to a potential of say 500 volts above this intersection potential, screen l4 will be subjected to a substantially constant potential gradient of 500 volts. By adjusting the potential applied to terminal ii to any desired value above the fixed upper intersection potential'of metal surface [5, any desired potential gradient or electric field can be produced and maintained across the light valve screen layer it,

It should be understood that the features of the invention explained above are equally applicable for color-television screens of the type as illustrated in Fig. 4.

The efiects just dgscribed as to creation of a defined electric field can also be obtained if the light transparent electrode I9 is omitted, particularly with smaller screens and in a manner as illustrated in Fig. 1. In all these cases a high positive potential to be applied to the reflector electrode and leading-in wire 2 I, can be dispensed with.

From the above it will be appreciated that the invention is concerned with reproducers of electric signals representative of intelligence of any kind impressed upon a cathode-ray or electron beam, in particular television reproducers, which include a screen the optical qualities of which to transmit or intercept visible light can be changed locally in accordance with those signals. intelligence thus represented in that screen is made visible to an observer from the outside by the combined eifect of screen portions the optical qualities of which are more or less changed or left unchanged, and visible day or room light incident upon the screen. The cathode ray beam upon which the signals are impressed, may be caused to move over the screen in order to afiect its optical qualities according to any desired course, and in particular swept over the screen in order to perform recurrent line and frame scanning motions. The screen may consist for instance of a layer of ionic crystal material of the type in which an impinging electron beam or.

stream creates opacity or color centers represented by loosely bound electrons which may travel in and across the layer under the influence of an electric field and be removed or dissipated by the latter or by another source of suitable quenching radiation, for instance infrared or heat radiation. In this case the screen is substantially transparent or translucent, and appears white to the observer with or without a reflecting backing, as the case may be, whereas areas affected by the cathode-ray beam appear with a darkness proportionate to the intensity of the cathode-ray beam.

The backing associated according to the invention with a cathode-ray controlled light valve screen, is either predominantly and highly light reflecting or scattering, or predominantly light absorbing.

From the above it will be appreciated that instead of excluding outside screen illumination as The in signal reproduction, particularly television systems heretofore known which require a darkened room, the invention utilizes this room inumination for the production of the screen picture. The screen should be illuminated as much as possible, either by daylight or byany artificial light, such as provided by room or reading lamps. The reproduction in the screen results from varying light reflecting or absorbing powers of the screen and can be observed to maximum advantage, the better the screen is illuminated and particularly a high degree of ordinary illuminating light,

whether day or artificial light, is provided; thus the disadvantage of observing the reproductions in a darkened room is avoided.

It should be understood that the invention is not limited to any exemplification hereinbefore described but to be derived in' its broadest aspects from the appended claims.

What I claim is:

1. In an apparatus utilizing incident visible light, particularly diffuse day or room light, for visibly reproducing intelligence represented in a screen by local changes of its qualities to transmit or absorb visible light incident upon it, in combination, a screen essentially comprised of ionic crystal material of the type which is permeable to visible light and in which an impinging electron beam which is modulated by signals representative of intelligence to be reproduced creates color centers which absorb visible light, and a backing associated with said screen essentially of aluminum, the thickness of said backing not exceeding about 5 microns in order to minimize absorption of impinging electrons, so that visible light incident upon and transmitted through portions of said screen instantaneously permeable to said light is reflected by said backing through such screen portions.

2. In a cathode ray tube including a cathode emitting electrons, means for directing the emitted electrons as a beam upon a screen within said tube, means for modulating the electron beam by signals representative of intelligence to be reproduced in said screen, said screen arranged to utilise incident visible light, particularly diiiuse day or room light, for visibly reproducing said intelligence, in combination: a translucent screen essentially of ionic crystal material in which an impinging electron beam can create color centers capable of absorbing visible light, means for producing a positive potential on the front side of said screen exposed to visible light and observation, and a backing of great optical reflecting power for visible light and pervious to electrons associated with the opposite side of said screen exposed to said electron beam, said backing of a material capable of emitting secondary electrons upon impingement by primary electrons at low ratio of the secondary to the primary emission for the velocity of the primary electrons of said impinging beam, so that the latter causes the accumulation of a negative charge on said backing until an equilibrium potential is produced thereon intermediate between said positive potential on the front side of said screen and the negative potential of said cathode.

3. In a cathode ray tube as set forth in claim 2, said backing essentially comprised of a substance of a. low ratio of secondary to primary electron emission and exemplified by carbon black, applied as a layer upon another thin metallic layer pervious to electrons and of high visible light reflecting power on the back of said screen.

4. A cathode ray tube adapted to utilize incident visible light, particularly difluse day or room light, for visibly reproducing fundamental partial color signals representative of intelligence, essentially comprising, in combination, means for developing a cathode ray beam, means for modulating said beam with said color signals to be reproduced, a screen upon which said modulated beam can impinge, said screen essentially of ionic crystal material which is permeable by visible light and in which an impinging electron beam can create color centers capable of absorbing visible light, a backing of optically high reflecting or scattering power for visible light associated with said screen so that visible light incident upon portions of said screen instantaneously permeable to said light is reflected by said backing through said screen portions, and a color filter composed of groups of fundamental partial color filters arranged in bands parallel to picture lines associated with said screen on its front side exposed to incident visible light and observation.

5. A cathode ray tube adapted to utilize incident visible light, particularly difiuse day or room light, for visibly reproducing signals representative of intelligence, essentially comprising, in combination, means for developing a cathode ray beam, means for modulating said beam with signals to be reproduced, and a self-supporting structure including a screen upon which said modulated beam can impinge and a backing of optically high reflecting or scattering power of visible light associated with said screen, said screen essentially of ionic crystal material which is permeable to visible light and in which an impinging electron beam can create color centers capable of absorbing such light so that visible light incident upon portions of said screen instantaneously permeable to such light is reflected through said screen portions.

6. A cathode ray tube adapted to utilize incident visible light, particularly difluse day or room light, for visibly reproducing signals representative of intelligence, essentially comprising, in combination, means for developing a cathode ray beam, means for modulating said beam with signals to be reproduced, a screen layer upon which said modulated beam can impinge, said layer essentially of ionic crystal material persaid screen layer instantaneously permeable to said light is reflected through said screen portions, and a frame-like support on which said backing and screen layer are mounted.

ADOLPH H. ROSEN'I'HAL.

REFERENCES CITED The following references are of record in the the of this patent:

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